Bind mounts disappear after Borg backup

What type of hardware are you using: Raspberry Pi 3, 4+
What YunoHost version are you running: 12.1.39 (stable)
How are you able to access your server: The webadmin
SSH

Describe your issue

Hello,

I’m experiencing an issue where specific bind mounts disappear after running a YunoHost Borg backup, while others remain intact.

Context:
I have a Raspberry Pi 5 running YunoHost with an external USB 3.0 HDD (3TB Toshiba) for additional storage. I’ve followed the external storage documentation to move data to this HDD using bind mounts.

My setup:
hdd mount: /dev/sdb1 mounted at /mnt/hdd

Bind mounts in /etc/fstab:

UUID="<uuid>" /mnt/hdd ext4 defaults,nofail 0 0
/mnt/hdd/yunohost/home/yunohost.backup /home/yunohost.backup none defaults,bind 0 0
/mnt/hdd/yunohost/home/yunohost.multimedia/share/Series /home/yunohost.multimedia/share/Series none defaults,bind 0 0
/mnt/hdd/yunohost/home/yunohost.multimedia/share/Video /home/yunohost.multimedia/share/Video none defaults,bind 0 0

Problem:
After the Borg backup completes successfully, the bind mounts for Series and Video disappear, but /home/yunohost.backup remains mounted.

Before backup:

$ lsblk
sdb      8:16   0   2.7T  0 disk 
└─sdb1   8:17   0   2.7T  0 part /home/yunohost.multimedia/share/Video
                                 /home/yunohost.multimedia/share/Series
                                 /home/yunohost.backup
                                 /mnt/hdd

After backup:

$ lsblk
sdb      8:16   0   2.7T  0 disk 
└─sdb1   8:17   0   2.7T  0 part /home/yunohost.backup
                                 /mnt/hdd

The backup itself succeeds without errors. From the Borg service journal, I can see it backs up data_multimedia (11GB) along with all apps.

The bind mounts can be manually restored with:

mount --bind /mnt/hdd/yunohost/home/yunohost.multimedia/share/Series /home/yunohost.multimedia/share/Series
mount --bind /mnt/hdd/yunohost/home/yunohost.multimedia/share/Video /home/yunohost.multimedia/share/Video
  • HDD health: Checked with smartctl - no errors, no reallocated sectors, UDMA_CRC_Error_Count: 0
  • dmesg: No USB disconnects, resets, or errors
  • Backup logs: Show successful completion for all backup items including data_multimedia: Success

Question:
Why do these specific bind mounts disappear after the Borg backup, while /home/yunohost.backup remains? Is the data_multimedia backup hook (/usr/share/yunohost/hooks/backup/18-data_multimedia) intentionally unmounting these directories without remounting them afterwards?

Thank you for any insights!

Share relevant logs or error messages

var/log/borg/260227_0818.log: https://paste.yunohost.org/raw/itonusawub
journalctl -u borg: https://paste.yunohost.org/raw/tekilusuhi
dmesg | grep -i “usb|reset|disconnect” | tail -50: https://paste.yunohost.org/raw/xewakudodi
smartctl -a /dev/sdb: https://paste.yunohost.org/raw/ajohavuliy

Hello again,

I’ve taken a closer look at the journal logs using journalctl:

It clearly shows that the two affected bind mounts (Series and Video) are being explicitly unmounted by systemd - along with several temporary mount points that are created during the backup process.

The mount units related to tmp-auto_data-data-multimedia are deactivated at the exact same timestamp, while /home/yunohost.backup itself remains mounted:

Mar 03 09:41:56 <usr> systemd[1]: home-yunohost.backup-tmp-auto_data-data-multimedia-share-Video.mount: Deactivated successfully.
Mar 03 09:41:56 <usr> systemd[1]: home-yunohost.backup-tmp-auto_data-data-multimedia-share-Series.mount: Deactivated successfully.
Mar 03 09:41:56 <usr> systemd[1]: home-yunohost.multimedia-share-Video.mount: Deactivated successfully.
Mar 03 09:41:56 <usr> systemd[1]: home-yunohost.multimedia-share-Series.mount: Deactivated successfully.
Mar 03 09:41:56 <usr> systemd[1]: mnt-hdd-yunohost-home-yunohost.backup-tmp-auto_data-data-multimedia.mount: Deactivated successfully.
Mar 03 09:41:56 <usr> systemd[1]: home-yunohost.backup-tmp-auto_data-data-multimedia.mount: Deactivated successfully.

You can find the relevant Yunopaste Link here.

This strongly suggests that something in the YunoHost backup workflow - possibly the data_multimedia backup hook - is explicitly unmounting these directories.

Since these mounts are defined in /etc/fstab, I would normally expect them to persist.

Has anyone observed similar behavior when bind-mounting subdirectories of yunohost.multimedia to external storage?

Thanks again!